1. Field of the Invention
The present invention relates to a cylindrical-shaped workpiece evaluation method and an evaluation apparatus therefor. More particularly, the present invention relates to a cylindrical-shaped workpiece evaluation method and an evaluation apparatus for evaluating a cylindrical-shaped workpiece based on a shape developed on a two-dimensional plane.
2. Description of Related Art
A conventional three-dimensional-shaped workpiece evaluation method for evaluating a three-dimensional-shaped workpiece by using a general three-dimensional measuring machine is known from JP-A No. H7-21238.
A general three-dimensional measuring machine used in the three-dimensional-shaped workpiece evaluation method is known from JP-A No. H5-99636 to perform measurement without contact with the three-dimensional-shaped workpiece, and from JP-A No. H10-175141 to perform measurement with contact with the three-dimensional-shaped workpiece.
These three-dimensional measuring machines have a moving member movable in x, y and z axial directions and a needle provided in the moving member. The machines measure the shape of the three-dimensional-shaped workpiece by bringing the needle into contact with the outer shape of the three-dimensional-shaped workpiece and detecting three-dimensional coordinates of the moving member during contact.
Furthermore, in the case of non-contact measurement, in place of the needle, a laser beam outputted from a laser unit is emitted on the three-dimensional-shaped workpiece so as to detect a distance from the three-dimensional-shaped workpiece. When the distance becomes a predetermined value, the coordinates of the laser unit are detected, to detect the shape of the three-dimensional-shaped workpiece. In the measurement by this three-dimensional measuring machine, a measurement value is obtained as coordinates of a point in an orthogonal coordinate system.
Upon evaluation of the three-dimensional-shaped workpiece by using the three-dimensional measuring machine, a three-dimensional-shaped workpiece as an evaluation reference is similarly set as a three-dimensional object by data in a three-dimensional orthogonal coordinate system.
Accordingly, the above-described conventional evaluation method obtains a pre-stored shape database based on a shape in the three-dimensional orthogonal coordinate system as an evaluation reference, and measurement data in the orthogonal coordinate system obtained by measuring the three-dimensional-shaped workpiece by the three-dimensional measuring machine, then reads the obtained measurement data and the shape data as an evaluation reference corresponding to the measurement data from the shape database, then extracts a point on the read shape data as the evaluation reference and a point on the measurement data corresponding to the point on the shape data, then calculates a distance between the corresponding points, thus performing evaluation on the three-dimensional-shaped workpiece. Furthermore, the method visually facilitates evaluation by color-coded display in correspondence with the distance between the points.
In the case of evaluation of a shape formed on a curved surface of a cylindrical-shaped member by the conventional three-dimensional-shaped workpiece evaluation method, shape measurement is also made in a three-dimensional orthogonal coordinate system space.
However, a flat shape including the position of a groove 21 (hereinbelow, also referred to as a xe2x80x9cgroove peripheral shapexe2x80x9d) formed in a curved surface of a cylindrical-shaped workpiece 20 schematically shown in FIG. 5, such as the shape of a shift drum used as a transmission for a motorcycle or the shape of a torque cam used as a belt type transmission for a motorcycle, can be designated with more advantage, not as figure data in a three-dimensional orthogonal coordinate system, but as a shape developed on a two-dimensional plane.
If the evaluation of a cylindrical-shaped workpiece is to be performed by the above conventional three-dimensional-shaped workpiece evaluation method, the measurement by the three-dimensional measuring machine and shape evaluation of the workpiece evaluation object are both based on three-dimensional orthogonal coordinates. Accordingly, it is necessary to convert figure data on a two-dimensional plane into a three-dimensional orthogonal coordinate system for correspondence with the measurement result in the three-dimensional orthogonal coordinate system. Furthermore, the evaluation result obtained in the three-dimensional orthogonal coordinate system cannot always be effectively used.
More specifically, as shown in FIG. 5, the groove peripheral shape of the groove 21 on the curved surface of the cylindrical-shaped workpiece 20 is determined by a surface function T(r, xcex8, l) in a cylindrical coordinate system. Note that r represents a radius of the cylindrical shape base. Assuming that a point on the edge of the cylindrical shape base opposite to a point (p) on the groove peripheral shape of the groove 21 is (Q), and the cylindrical-shaped workpiece 20 is placed on an xy plane with the central point of the cylindrical-shaped workpiece 20 corresponding to the origin of the xy coordinates, represents an angle between the axis x and the point (Q) on the edge of the cylindrical shape base; (r, xcex8), a position in polar coordinates on the xy plane defining the point (Q) on the edge; and l, a length of the normal from the point (p) to the point (Q).
However, in the cylindrical-shaped workpiece 20, in a case where the position of the point (p) on the curved surface of the cylindrical-shaped workpiece 20 is significant, i.e., the position of the point (Q) on the edge and the length (l) from the point (Q) to the point (p) in the axial direction of the cylindrical-shaped workpiece 20 are significant, but the position of the base of the cylindrical-shaped workpiece 20 in the radial (r) direction is not so significant, if three-dimensional-shaped workpiece evaluation is performed based on measurement by a three-dimensional measuring machine which handles the position (x, y, l) of the respective points on the groove periphery as the position (x,y, z) in a three-dimensional orthogonal coordinate system, the three-dimensional-shaped workpiece evaluation based on the measurement result by the three-dimensional measuring machine is performed regardless of the above features of the cylindrical-shaped workpiece 20. Thus the absolute value is erroneously displayed at the same ratio in every direction in the three-dimensional orthogonal coordinate space. Such erroneous display effects correct evaluation and increases the number of process steps.
An object of the present invention is to provide an evaluation method and an evaluation apparatus for a cylindrical-shaped workpiece designated as a shape developed on a two-dimensional plane.
The cylindrical-shaped workpiece evaluation method of the present invention comprises:
a first step of reading two-dimensional reference shape data based on a two-dimensional shape designated by designation means from storage means holding plural two-dimensional reference shape data based on a two-dimensional shape displayed on a two-dimensional plane where a curved surface of a reference cylindrical-shaped workpiece is developed;
a second step of converting the reference cylindrical-shaped workpiece having a two-dimensional-shaped curved surface corresponding to the two-dimensional reference shape data read at said first step into a surface shape of said reference cylindrical-shaped workpiece;
a third step of measuring a surface shape of an evaluation object cylindrical-shaped workpiece and obtaining a distance between a measurement point in said measurement and a point in the surface shape of the reference cylindrical-shaped workpiece converted at said second step, corresponding to said measurement point; and
a fourth step of overlay-displaying the distance obtained at said third step as an error on the two-dimensional shape corresponding to the two-dimensional reference shape data read at said first step,
wherein the evaluation object cylindrical-shaped workpiece is evaluated based on the two-dimensional display where the error is overlay-displayed at said fourth step.
The cylindrical-shaped workpiece evaluation apparatus of the present invention comprises:
storage means for storing plural two-dimensional reference shape data based on a two-dimensional shape displayed on a two-dimensional plane where a curved surface of a reference cylindrical-shaped workpiece is developed;
designation means for designating one two-dimensional reference shape data read from said storage means based on the two-dimensional shape;
conversion means for converting the reference cylindrical-shaped workpiece having a curved surface having a two-dimensional shape corresponding to the two-dimensional shape data read from said storage means into a surface shape of said reference cylindrical-shaped workpiece;
calculation means for measuring a surface shape of an evaluation object cylindrical-shaped workpiece and obtaining a distance between a measurement point in said measurement and a point in the surface shape of the reference cylindrical-shaped workpiece converted at said second step, corresponding to said measurement point;
display control means for overlay-displaying the distance obtained by said calculation means as an error on the two-dimensional shape corresponding to the two-dimensional reference shape data read from said storage means, p1 wherein the evaluation object cylindrical-shaped workpiece is evaluated based on the two-dimensional display where the error is overlay-displayed.
According to the cylindrical-shaped workpiece evaluation method and evaluation apparatus of the present invention, one two-dimensional reference shape data is substantially designated and read from the storage means holding plural two-dimensional reference shape data based on a two-dimensional shape displayed on a two-dimensional plane where a curved surface of a reference cylindrical-shaped workpiece is developed. A reference cylindrical-shaped workpiece having a curved surface with a two-dimensional shape corresponding to the read two-dimensional reference shape data is converted to the surface shape of the reference cylindrical-shaped workpiece.
On the other hand, the surface shape of the evaluation object cylindrical-shaped workpiece is measured, and the distance between a measurement point by the measuring machine and a point in the surface shape of the reference cylindrical-shaped workpiece corresponding to the measurement point is obtained. The obtained distance is overlay-displayed as an error on the two-dimensional shape corresponding to the two-dimensional reference shape data read from the storage means. The evaluation object cylindrical-shaped workpiece is evaluated based on the two-dimensional display where the error is overlay-displayed.
According to the cylindrical-shaped workpiece evaluation method and evaluation apparatus of the present invention, a cylindrical-shaped workpiece designated with a shape developed on a two-dimensional plane can be easily and accurately evaluated.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.